[clang] [HLSL] Implementation of the fmod intrinsic (PR #108849)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

We should announce `__builtin_elementwise_fmod`  here: `clang/docs/ReleaseNotes.rst`
See @spall  PR where we just did this: https://github.com/llvm/llvm-project/pull/108121/files

https://github.com/llvm/llvm-project/pull/108849